This invention relates generally to the fabrication of integrated circuits and, particularly, to the fabrication of integrated circuits with extremely low dielectric constants.
Low dielectric constant materials are used as interlayer dielectrics in semiconductor devices to reduce the RC delay and improve device performance. As device sizes continue to shrink, the dielectric constant of the material between metal lines must also decrease to maintain the improvement. The eventual limit for dielectric constant is k=1, which is the value for a vacuum. This can only be obtained by producing a void space between metal lines, equivalent to creating a so-called air gap. The air itself has a dielectric constant very near 1.
One major issue facing air gap technology is how to remove sacrificial material to facilitate multi-layer structures. Plasmas may be destructive to the metal lines. Wet etches have many problems including capillary forces that can break the lines apart, difficulty in removing material from small features, and difficulty in removing the wet etch chemical once it has been introduced. Thermal decomposition presents a challenge in that the sacrificial material must remain stable during high temperature fabrication steps, but then decompose rapidly at temperatures that will not destroy the rest of the device.
Thus, there is a need for better ways to form openings within integrated circuits.